Effects of Root and Foliar Application of Rainbow Trout-Derived Protein Hydrolysates on the Postharvest Quality of Tomato Fruit During Cold Storage

This two-year study evaluated the effects of rainbow trout (Oncorhynchus mykiss) waste-derived protein hydrolysates (HYDs), applied to the roots or foliage of soilless-grown tomato plants at 0.2 (HYD1), 0.4 (HYD2) and 0.8 g L−1 (HYD3), on fruit quality during 28 days of cold storage under modified-atmosphere packaging. Because year × treatment interactions were significant, each year was analyzed separately. In both years, HYD treatments reduced weight loss and respiration rate and maintained firmness compared with the control. Root-applied HYD1 was the only treatment that maintained higher firmness than the control from day 7 to day 28 in both years, and it had the highest overall quality index in a multi-criteria (TOPSIS) evaluation at the end of storage in both years. In contrast, the effects on soluble solids, titratable acidity, vitamin C, lycopene, anthocyanins, phenolics, flavonoids and antioxidant activity depended on the year, and vitamin C and lycopene responded in opposite directions in the two years. Fish-waste HYDs, particularly root-applied HYD1, are therefore promising for maintaining firmness and reducing postharvest losses of tomato, whereas their effects on bioactive compounds require further multi-season evaluation.